Receiving apparatus



July 2 19m" c. H. BRASELTQN RECEIVING APPARATUS Filed July 2s, 19:5*1

AT1-ox zN'EYs Patented July 2, 1940 UNITED STATES PATENT OFFICE Chester H. Braselton, New York, N. Y., assignor to National Television Corporation, Wilmington, Del., a corporation of Delaware E Application July 2s, 1937, s`e'ra1'N..156,060

claims. (o1. 25o-'20) This invention relates to radio receiving apparatus and has, for its principal object, to provide an apparatus which is highly selectivev and at the same time will faithfully reproduce substantially all of the desired signalfrequencies with little or no attenuation.

Another object of the invention is to provide .a radio receiver in whichinterference from stations on either side of the selected station is reduced toa minimum.

Another object of the invention is to provide a receiver in which the signal frequencies are reproduced by the beats between the incoming radio frequency oscillations and an `independ- 15 ently controlled oscillation corresponding to the carrier frequency.

Another robject of the invention is to provide a radio receiver with means yto independently control the level of the carrier frequency with respect to that of the side bands.

Other objects of the invention will be apparent yas the description thereof proceeds.

The invention is illustrated in the accompanying drawing, the single figure of which represents a circuit diagram of a receiver embodying the invention.

In transmitting intelligence by radio a carrier wave with its accompanying side bands is selected at the receiver by means of 'resonantcircuits which tend to increaseL the carrier frequency andfattenuate those frequencies farthest away from the carrier. The greater the selectivity the more this attenuation is carried out, with the result that a highly selective receiver may tend to completely cut off high frequency notes of the signal.

This invention comprehends the reception of a band of frequencies wide enough to include the carrier and all necessary side band frequencies, v the division of this received energy into two paths, the eliminationrof substantially al1 frequencies in one of said paths except'the carrier frequency, the combination of the paths again in a single circuit to cause the separated carrier frequency to coact with the transmitted frequencies in the other path to reproduce'` the audio signal. I prefer to'provide the single circuit with two therrnionic tubes with their plate circuits in series and to connect one of said paths to the grid of one tube, while the other path is connectedl to the grid of the other tube.

Referring to the figure, I have shown the circuit in connection with a super-heterodyne in which the tuner and radio frequency amplifier unit Imay be used tofselect the desiredband of frequencies in accordance with the usual practice an'dto amplify them -prior to introducing them to the mixer tube, which is Icontained in the unit II, together with the local oscillator and intermediate frequency amplifier stages. 5

`The output circuit for the unit II may contain a coil I2 which may be coupled toa coil I3, tuned by avariable condenser I4. One end of this coilr and condenser combination may Ibe connected to the control grids I5 and I6 of pentode tubes L10 I'I and I8, respectively, whilethe otherrend of the coil and condensrmay be connected to an ,automatic volume control circuit I9, to be subsequently described, for supplying a controlled bias to the grids of the tubes. The units I0 and 15 II may dier from ordinary unitsof this nature n solely .by virtue of the fa'ct that they vare both 'preferably tuned lsufficiently broad to pass as uniformly as possible `the entire band of frequencies necessary to produce the maximum sigz.20 nalfrequency desired. In other words, if 16,000 cycles" is the Imaximum signal frequency which is to be vused with the carrier, then the units I0 and II should preferably be designed to pass A16,0010 cycles on each side I of the carrier, or,,-25

where single sideband transmission is to be used, on .one side` of the carrier.

The tubes I1 and, IB represent the first tubes .in `the two paths for dividing the signal, the

former being in the broadly tuned Ipath, while 30 the latter is in the sharply tuned'path. The

tube I'I may have itssuppressor grid 20 connected to the cathode 2|.;which may be grounded through a resistance 22 shunted by a condenser 23, while the screen grid 24 may be given a posi- 35 tive -potentiahindicated atr 25. Acondenser 26 may -be 'connected between the .screen grid and the cathode. .The anode '21 of` thetube I 'I may be connected to a coil 28 and condenser 28, forming a `resonant circuit, the other end of 40 which may be connected-.to a source of positive potential, indicated at 38. A coil 3l, tuned by la variable condenser 32, may be -inductively lcoupled Yto the coil 28 and may have one end connected to the control grid 33 of a tube 34. I 45 This tube 34 maypreferably be of the` three element type having an anode 35 and a cathode 36, and may form one of the Ytwo Vseries connected tubes used for kcombining the two signal paths. The 'control grid 33 may be given a nega- 50 tive potential by means of a potentiometer 38 Vand-battery y39, which may be connected between-the cathode 3 6 jo-fthe tube and the opposite Vends of the coil r3l and condenser-32. In-

,asmuchgas-the-tube is-.maintained above ground, 55

there should preferably be provided a separate source of heating current for the tube.

The tuned circuits formed by the coils 28 and 3| and condensers 29 and 32 are preferably broad enough to permit all of the signal to pass without attenuation, as has already been stated in connection with the circuits of the units I and Hence, the grid 33 has applied to it a variable voltage corresponding to the entire signal together, perhaps, with some side band fregrid 41 may be given a positive potential 48 and a by-pass condenser 49 may be connected between `the screen grid and the cathode. The anode 59 of the tube may be given a positive potential, indicated at through a resonant circuit 52, which may be coupled to a resonant circuit 53 connected to the grid 54 of the tube 4D. This tube 48 may also be of the pentode type with the connections made exactly the same as those just described for the tube I8.

The output circuit of the tube may comprise the resonant circuit 55 which may be coupled to a resonant circuit 56 connected between the control grid 51 of the tube 4|, and the cathode 58 of that tube through a potentiometer 59 shunted by a battery 5E), so as to give an adjustable negative potential to the grid 51. A condenser 6| may be connected between the cathode and the potentiometer end of the resonant circuit 56. The screen grid 62 of the tube 4| may be given a positive potential as indicated at 63, while a condenser 54 may be connected between the screen grid and the cathode.

The tube 4| preferably acts as a limiting tube to maintain the voltage delivered to the subse- `quent part of the circuit below a certain maximum under all conditions, and hence I prefer to give the anode 85 a low potential of 22.5 volts, as indicated at 56, while the screen has a voltage of approximately 100 volts. The anode circuit contains resonant circuit 61 which may be inductively coupled to a coil 58. The coil B8 may be shunted by a variable condenser 69 and the midpoint of the coil grounded, as indicated at 10.

One side of the coil 68 and condenser 59 may be connected through a piezo electric crystal 1| to the grid 12 of the tube 42. The other end of the coil 88 and condenser 69 may be connected `through a variable condenser 14 to the grid 12, so

that the coil 58 and condenser 59, crystal 1| and condenser 14 form a bridge circuit, one terminal of which is the ground connection at 18, while the other terminal is the grid 12, the crystal 1| and condenser 14 being in opposite legs of the bridge, and the latter having sufficient value to balance the capacity of the former. The grid 12 of the tube 42 is also connected through a resistance 15 and a potentiometer 16 and battery 11 to the cathode 18 of the tube and to ground, there being a condenser 19 across the battery and potentiometer.

This circuit is intended to feed to the grid 12 of the tube 42 a variable voltage corresponding to the carrier frequency only of the inter- `cepted signal without any of the side band frevtween this screen grid and cathode 18.

quencies. Accordingly, the resonant circuits 52, 53, 55, 56, 61, and 68 are preferably made as sharp as possible. By means of the crystal 1|, which, in the present instance, may be cut to respond to the intermediate frequency only, all frequencies, save this particular frequency, will be eliminated from this sharp circuit, and the grid 12 will therefore receive oscillating voltage only when the receiver is tuned exactly on a carrier so that the signal will be present in the sharp circuit.

The tubes 34 and 42 are arranged with their plate circuits in series, as has already been stated, and to this end the plate of the tube 42 may vbe `connected directly to the cathode 40 of the tube 34, while the plate 35 of this tube may be connected through a load resistance 8| and plate potential battery 82 to the cathode 18 of the tube 42. The suppressor grid 83 of the tube 42 may be connected to the cathode 18 and the screen grid 84 may be given a positive potential on the battery 82. A condenser 85 may be connected be- I may prefer to connect an audio amplier 86 across the resistance 8|, while the output of the amplifier may be connected to any translating device, such as the speaker 81.

The tube 34 is provided with a suitable bias for its grid circuit by means of the potentiometer 38 and battery 39 so that this tube acts as nearly as possible as an R. F. amplifier, reducing detection in the tube 34 to a minimum. The plate voltage of the tube 34 is dependent not only upon the battery 82, but also upon the plate current of the tube 42, which is controlled by the carrier oscillation delivered to its grid. The tube 42 is also adjusted as to grid bias by means of the potentiometer 16 and battery 11 so as to have a minimum of detector action, and inasmuch as this is operated as a pentode, variation in plate potential caused by the action of the tube 34 has little or no effect on the plate current of this tube. The tube 34, however, connected to operate as a triode, is sensitive to plate voltage variation, and hence its plate-cathode current will vary not only in accordance with the grid voltage variation, but also in accordance with the plate cathode current of the tube 42, and there will be beats produced between the carrier oscillation introduced into the series circuit by the tube 42 and the complete broad band of os-V cillations introduced into the circuit by the tube 34. These beats result in the audio signal which may be transferred to the audio amplifier 86 by means of the drop in potential across the resistance 8|.

I have found that with my improved circuit the relation of the levels of the broad and sharp signals is important, and I therefore preferably provide an automatic volume control to maintain a substantially constant level for all signals lntercepted by the receiver. To this end the diode tube 88, having an anode 89 and a cathode 90 may be used. The anode 89 may be connected to the grounded cathode 99 through a high resistance 9|, and signal potential may be supplied to the tube by connecting the anode 88 to the grid 51 of the tube 4| through a large capacity condenser 92. The anode 89 may also be connected through a large resistance 93 to the automatic` volume control circuit I9 while a by-pass condenser 94 may be connected between this circuit and ground. The drop in potential across the resistance 8| as controlled by the diode tube 88 changes the potential on the grids of the tubes acceptor If1`andv It: and of the tubesiin' the: unit lil, as willl be lm'derstood. Y

I have alsofoundl thatl best results are ob"- tained when theflevel of the sharp'- circuit isnot permitted 'to exceed a'- certain maximum which' When' there is no' signal onA the grid of the tubel2Jv therey is'noK variable current owing in the series circuit except the amplied radio frequenciesA of 4the-tubeSlL and' hence no beats are produced the tube 3'4", and there will be' no audioA output from-the circuit. .I-nasmuch as the crystal 'H is ground to respond only to the intermediate4 frequency, which may be in the neighborhood' of 470' kilccycles, no signal will be applied tothe grid of the tube t2 unless the receiver is tuned' to a carrier which will produce the properv oscillationy to affect the crystal.

Hence, the set must be' tuned exactly on the desiredcarrier before there is any soundV produced bythe speaker, and the instant the set is tuned to one side or the otherof the carrier the strength of' the carrier oscillation falls off sufliciently in the' sharp circuit to immediately stopthe circuit from operating. The effect of the circuit, therefore, is extremely sharp. tuning while at the same time' all of the desired' signal frequencies may be received without attenuation owing to the broad flat topped! resonance curve of the broad circuit including the tubes I Tand.- 34.

While the invention has been shown with a superheterodyne receiver, it will be evident. that. other typesof receivers may be used embodying 'the same principle, although the use of an intermediate frequency makes the construction and operation simpler, inasmuch as the tuning ofl broad andsharp stages does not have to be changed but. may be fixed: at the intermediate 4frequency, and the crystal may be ground to that-one frequency; n

Whilea'- crystal has been showny for eliminating` all but the carrier frequency in' the sharp circuit, other methods may be used, if desired;

also. under certain conditions it may not be necessary toy sharpen the circuit to such a degree,v and Vcoupled resonant circuits may be found satisfactory forthis. purpose. However, as it is `very diicult, with tubes of present construction toentirelyeliminate rectification, owing to the difliculty of producing a tube with a straight line characteristic curve, better results may be obtained' if the sharp vcircuit produces the car rier frequency alone.

from the spirit of the invention,A such. as prof viding automatic volume control by other well knownv methods, and' I therefore desire, to claim` of the appended claims.

1*. A receiving apparatus comprising fre-r quency-selecting means-capable of passing awide band of frequencies equal to at least the maximum signal frequencyto be received, means to separate the signal received by said means into two paths,` one of said paths being arranged toI pass substantially the entire selected band of frequencies, means associatedy with the other path to limit' the `frequency therein to substantially' a single frequency', a' pairv ofV thermionic tubes each having input and output circuits and with their output circuits connected in series',

meansl to` apply voltage from-fone of said pathsv to the input circuit of one of saidtubes', meansv to apply voltage from the other of said paths to theinput circuit of the other of saidl tubes, and means to translate the output current of said tubes into an intelligible signal.

2. A 4receiving' apparatus comprising frequencyeselecting means capable of passingA a wide band' of frequencies equal: to at least the maximum signal frequency to be received', meansV toy separate the signal'received' by said means into two paths, one of' said paths being arranged to pass4 substantially the entire selected bandA ofv frequencies, means associated with the other path to limit the frequencyvtherein to substantiall'y' afsinglel` frequency, a: pair'of' thermionic tubes each having'input-and'output circuits and withtheir output circuits connected in series, means to apply voltage froml one of said paths to the input circuit of onefof said tubes; means to1 apply voltage from the other of said pathsto the' input circuit of the other ofy 'saidftubea means to translate the output current of" said" tubes into an intelligible signal, and means to maintain' a substantiallyy constant level ofv signals inboth` paths regardless of 'the strength'- of'l the intercepted signali 3. A receivingl apparatuscomprising frequencyselectingr means capable of passing awide band' of frequencies'equal' to at least the maximum signal frequencyl to be received, means to separate-the signal received by said means into two paths, oneof said'paths being arranged topass substantially the entire selected band of frequencies, means associated with the other `path to limit the frequency therein to substantially/a singlefrequency, a pair of thermionic tubes each having input and' output circuits and with their output circuits connected' in series, means to apply voltage from one of said paths to the input'circuit of one of said tubes, means to apply voltage `from the other of said paths to the input circuit'of the' other of said tubes, means to translate the outputcurrent of said tubes into an intelligible signal, and means to limit the voltage delivered by said single frequency path to a predetermined maximum.-

4. A receiving apparatus comprising frequency-selecting' means capable of passing a wide band of frequencies equal to at least the maximum signal frequency to be received,` means to separate -the energy selected by said selecting means` into two paths, one of said paths being arranged to. pass substantially the entire selected bandlof frequencies, means associated with said other path to limit the frequency therein to substantially asingle frequency, a pair of thermionic tubes eachr having an. input circuit and an output circuit withi the output'circuits of said tubes; connected. inseriesu means to, apply voltage.

the invention' broadly, limited only by the scope arf est

from one path to the input circuit of one of said tubes, means to .apply voltage from said other path to the input circuit of said other tube, means to operate said tubes with a minimum y of detector action, and means to translate output currents from said tubes into intelligible signals.

5. A receiving apparatus comprising frequency-selecting means capable of passing a wide band of frequencies equal to at least the maximum signal frequency to be received, means to separate the energy selected by said selecting means into two paths, one of said paths being arranged to pass substantially the entire selected band of frequencies, means associated with said other path to limit the frequency therein to substantially a single frequency, a pair of thermionic tubes each having an input circuit and an output circuit with the output circuits of said tubes connected in series, means to apply voltage from one path to the input circuit of one of said tubes, means to apply voltage from said other path to the input circuit of said other tube, means to operate said tubes with a minimum of detector action, means to translate output currents from said tubes into intelligibile signals, and means to maintain a substantially constant level in both said paths for any intercepted signal.

6. A receiving apparatus comprising frequency-selecting means capable of passing a wide band of frequencies equal to at least the maximum signal frequency to be received, means to separate the energy selected by said selecting means into two paths, one of said paths being arranged to pass substantially the entire selected band of frequencies, means associated with said other path to limit the frequency therein to substantially a single frequency, a pair of thermionic tubes each having an input and an output circuit with the output circuits of said tubes connected in series, means to apply voltage from one path to the input circuit of one of said tubes, means to apply voltage from said other path to the input circuit of said other tube, means to operate said tubes with a minimum of detector action, means to translate output currents from said tubes into intelligible signals, and means to limit the amplitude of oscillations produced by the said single frequency path below a predetermined maximum.

7. A receiving apparatus comprising frequency-selecting means capable of passing a wide band of frequencies equal to at least the maximum signal frequency to be received, means to separate the signals received by said means linto two paths, one of said paths being arranged to pass substantially the entire selected band of frequencies, means associated with the other path to limit the frequency therein to substantially a single frequency, a pair of thermionic tubes each having input and output circuits and with their output circuits connected in series, means to apply voltage from one of said paths to the input circuit of one of said tubes, means to apply voltage from the other of said paths to the input circuit of the other of said tubes, means to translate the output current of said tubes into an intelligible signal, means to maintain a substantially constant level in said paths, and means to limit the voltage delivered by said single frequency path to a predetermined maximum.

8. A receiving apparatus comprising. frequency-selecting means capable of passing a Wide band of frequencies equal to at least the maximum signal frequency to be received, means to separate the signal received by said means into two paths, one of said paths being arranged to pass substantially the entire selected band of frequencies, means associated with the other path to limit the frequency therein to substantially a single frequency, a pair of thermionic tubes each having input and output circuits and with their output circuits connected in series, means to apply voltage from. one of said paths to the input circuit of one of said tubes, means to apply voltage from the other of said paths to the input circuit of the other of said tubes, means to operate said tubes with a minimum of detector action, means to translate the output current of said tubes into intelligible signals, means to maintain a substantially constant level in both said paths for any intercepted signal, and means to limit the amplitude of oscillations produced by the said single frequency path below a predetermined maximum.

9. A receiving apparatus comprising frequency-selecting means capable of passing a Wide band of frequencies equal to at least the maxlmum. signal frequency to be received, means to separate the energy received by said frequencyselecting means into two paths, one of said paths being arranged to pass substantially the entire selected band of frequencies, means associated with said other path to limit the frequency therein to substantially a single frequency, a thermionic tube having an anode, a cathode and a control electrode, means to apply voltage from said broad path between said control electrode and cathode of said tube, means to bias said control electrode so that said tube will operate with a minimum, of detection, a second thermionic tube having a cathode, a control electrode and an anode, means to effectively shield the control electrode of said second tube from the anode thereof, means to apply voltage from said single frequency path between the control electrode and cathode of said second tube, means to connect the anode circuits of said tubes in series, a source of anode potential included in said series circuit, and a load circuit associated with said series circuit.

10. A receiving apparatus comprising frequency-selecting means capable of passing a wide band of frequencies equal to at least the maximum signal frequency to be received, means to separate the energy received by said frequencyselecting means into two paths, one of said paths being arranged to pass substantially the entire selected band of frequencies, means associated with said other path to limit the frequency therein to substantially a single frequency, a thermionic tube having an anode, a cathode and a control electrode, means to apply voltage from said broad path between said control electrode and cathode of said tube, means to bias said control electrode so that said tube will operate with a minimum of detection, a second thermionic tube having a cathode, a control electrode and an anode, means to effectively shield the control electrode of said second tube from the anode thereof, means to apply voltage from said single frequency path between the control electrode and cathode of said second tube, means to connect the anode circuits of said tubes in series, a source of anode potential included in said series circuit, a load circuit associated with said series circuit, and means to maintain a constant level for both of said paths regardless of the signal intercepted by said receiver.

11. A receiving apparatus comprising frequency-selecting means capable of passing a wide 'lol band of frequencies equal to at least the maximum signal frequency to be received, means to separate the energy received by said frequencyselecting means into two paths, one of said paths being arranged to pass substantially the entire selected band of frequencies, means associated with'said other path to limit the frequency therein to substantially a single frequency, a thermionic tube having an anode, a cathode and a control electrode, means to apply voltage from said broad path between said control electrode and cathode of said tube, means to bias said control electrode so that said tube will operate with a minimum of detection, a second thermionic tube having a cathode, a control electrode and an anode, means to effectively shield the control electrode. of said second tube from the anode thereof, means to apply voltage from said single frequency path between the control electrode and cathode of said second tube, means to connect the anode circuits of said tubes in series, a source of anode potential included in said series circuit, a load circuit associated with said series circuit, and means to limit the voltage applied to the grid of said second tube to below a predetermined maximum.

12. A receiving apparatus comprising frequency-selecting means capable ofv passing a wide band of frequencies equal to at least the maximum signal frequency to be received, means to separate the energy received by said frequencyselecting means into two paths, one of said paths being arranged to pass substantially the entire selected band of frequencies, means associated with said other path to limit the frequency therein to substantially a single frequency, a thermionic tube having an anode, a cathode and a control electrode, means to apply voltage from said broad path between said control electrode and cathode of said tube, means to bias said control electrode so that said tube will operate with a minimum of detection, a second thermionic tube having a cathode, a control electrode and an anode, means to effectively shield the control electrode of said second tube from the anode thereof, means to applyvoltage from said single frequency path between the control electrode and cathode of said second tube, means to connect the anode circuits of said tubes in series, a source of anode potential included in said series circuit, a load circuit associated with said series circuit, means to maintain a constant level for both of said paths regardless of the signal intercepted by said receiver, and means to limit the voltage applied to the grid of said second tube to below a predetermined maximum.

13. A receiving apparatus comprising frequency-selecting means capable of passinga wide band yof frequencies, means to separate the energy received by said selecting means into two paths, oner of said paths being sharper thanthe other, apair of thermionic tubes having input circuits and output circuits with their output circuits connected in series, means to apply voltage from one path to the input circuit of one tube, means to apply voltage from the other path to the input circuit of said other tube, and means to transmit into an intelligible signal currents flowing in said series output circuit.

14. A receiving apparatus comprising frequencyselecting means capable of passing a wide band of frequencies, means to separate the energy received by said selecting means into two circuits and output circuits with their output circuits connected in series, means to apply voltage from one path to the input circuit of one tube, means to apply voltage from the other path to the input circuit' of said other tube, means to transmit into an intelligible signal currents flowing in said series output circuit, and means to maintain a substantially constant level in said two paths for any signal received.

15. A receiving apparatus comprising frequency-selecting means capable of passing a wide bandof frequencies, means to separate the energy received by said selecting means into two paths, one of said paths being sharper than the other, a pair of thermionic tubes having input circuits and output circuits with their output circuits connected in series, means to apply voltage 

